This invention relates to audio signal compensation techniques and, more particularly, to mobile communication devices with audio signal adaptation for hearing characteristics of the listener.
As people age, hearing ability often deteriorates. A common type of age-related hearing problem is reduced sensitivity of the ear to the higher end of the speech frequency range. For the elderly with this type of hearing loss, following a conversation is difficult. This problem is exacerbated when using a telephone because there is no visual feedback, unlike that present in face to face conversation. In fact, most listeners are not able to discriminate speech solely by hearing if the listener""s formant discrimination ability is less than half a normal listener""s. Formant discrimination is the ability to distinguish the sounds (formants) that compose a particular speech sound.
Speech signals consist of different kinds of acoustic cues covering the frequency range of 0.1 kHz to 8 kHz. This frequency range is within the normal hearing sensitivity curve, which is often described as the speech banana due to the shape of the curve. All the acoustic cues in speech (e.g., fundamental frequency, vowel formants, noise bursts, transitions, etc.) lie within the speech banana. The most important part of the banana is the middle region, approximately 0.5 kHz to 2 kHz. This middle region carries most of the phonetically important information in speech. For example, the higher (over 3 kHz) formants in vowels can be destroyed largely without any significant effects on the intelligibility of speech signals. If, however, formants in the middle range are destroyed or covered by noise, the intelligibility of a speech signal is seriously decreased.
Unfortunately, mobile communication systems have generally not recognized the problems caused by destruction of formant information in the middle region of the speech banana. Often, due to the destruction of middle region formants, it is hard for even a listener with normal hearing to understand spoken messages via a telephone. Listeners with hearing loss are at an even greater disadvantage because the visual cues that they commonly use to compensate are not present in phone conversations.
Many people have high frequency hearing loss. These people generally have lost some ability to hear the upper end of the middle region of the speech banana. The most usual reason for not being able to discriminate higher frequencies in speech is decreased hearing ability caused by aging (presbyacusis) or noise injury. Because female voices are generally higher in frequency than male voices, it is commonly difficult for older listeners to understand female voices.
Hearing defects caused by presbyacusis or noise injury are quite common. Presbyacusis of varying degrees develops in everyone as they age. Familiar sources of noise injury that may cause permanent hearing damage in the speech frequencies are jet engines, rock concerts, and industrial equipment.
Often, users of mobile communication systems are forced to communicate by speech in environments where background noise of high or low frequencies selectively masks important information in their speech. This background noise interference will reduce the hearing capability of even a person having normal hearing ability. Because telephone conversations decrease the intelligibility of speech even in listeners with normal hearing, presbyacusis and noise injury further worsen the quality of speech intelligibility in telecommunications.
Disclosed is a method and apparatus for increasing the intelligibility of speech in mobile communications. Transposing some of the acoustic information bearing parameters of speech in the frequency domain modifies a speech signal so that intelligibility can be increased for listeners suffering from presbyacusis, noise injury, or other hearing impairments.
To compensate for presbyacusis, noise injury, high background noise, or other causes of hearing impairment, the critical frequencies in the speech signal can be shifted in the frequency domain in such a way that the information bearing elements of the speech signal remain unchanged in relation to each other. For example, to compensate for a listener""s presbyacusis, the shifting of speech signal information is towards lower frequencies in a manner that all or a part of the speech range is moved to a frequency band that is more suitable for the listener.
In a presently preferred embodiment of the invention, a mobile station is disclosed that processes a received audio signal such that acoustic cues important to speech intelligibility are transposed in the frequency domain to account for a listener""s unique hearing ability or to compensate for background noise. The mobile station may use a predetermined hearing profile for the listener, perhaps obtained from listener""s audiologist, may create a listener profile by administering a hearing test, may allow the user to select a profile from a menu of predetermined profiles, or may allow the user to create his own profile by entering information via the user interface. In alternative embodiments, background noise either in the speaker""s environment or in the listener""s environment may be counteracted by shifting the voice signal away from the frequencies of the background noise. In another alternative embodiment, the mobile communications network could perform all the signal processing necessary to implement the disclosed innovations, thereby saving mobile station battery and processing power. In some embodiments, user profiles could also be stored on the communication network in order to save mobile station memory and to allow users to freely switch between mobile stations without having to recreate a listener profile.